The ratio of pressure to output variable may be different between pressure sensors according to manufacture. This relates to both static ratio fluctuations, the different behavior at different static pressures, and differences in the dynamic behavior, that is to say differences between different pressure sensors in terms of their frequency response at dynamically changing pressures.
In order to arrive at a correct assessment of the output variable, there is therefore a need to calibrate the pressure sensor in terms both of its static and of its dynamic behavior. The invention described below relates to calibrating the dynamic behavior of pressure sensors.
Calibration is understood to mean a method in which the deviation of a sensor from a normal is determined in a first step, so as, in a second step, to use the determined deviation in the subsequent use of the sensor in order to correct the values determined thereby.
It is known to dynamically calibrate vibration sensors, inter alia by way of the service provided by the applicant. In this case, a vibration sensor to be calibrated is excited by narrowband or broadband signals. In narrowband excitation, the vibration sensors are excited with a sinusoidal signal that is as undisturbed as possible. In broadband excitation, the vibration sensors are generally excited with impacts.
During excitation with sinusoidal signals, the response, for example the voltage output U of the vibration sensor, is able to be measured. This is put into a ratio, with the known excitation, that is to say the acceleration a, and the sensitivity of the sensor is obtained:
  s  =            U      a        =                  [                  V                      m            ⁢                          /                        ⁢                          s              2                                      ]            .      
Due to the construction principle of the vibration sensor, this sensitivity is however dependent on the frequency. If the frequency of the excitation is varied, the frequency response of the vibration sensor may be recorded as is illustrated in FIG. 1. The frequency response assists in evaluating the frequency up to which the vibration sensor is able to be used in a real measurement application, and the frequency from which deviations in the measured values have to be taken into consideration.
In metrology, a distinction is drawn between two types of calibration, secondary and primary calibration.
The known determination of the frequency response of a vibration sensor is performed through a primary calibration.
In primary calibration, the physical variable that is sought is calculated from other variables. If it is intended for example to determine the mass of a fluid in a primary manner, then the density ρ thereof may be measured or determined as a material constant from tables, and the volume V of the fluid may be measured. The mass m is able to be calculated using the equationm=V·ρ. 
The variables entering into the equation are in this case generally able to be determined very accurately and ensure that the variable to be determined is able to be calculated very accurately.
In a secondary calibration, only two variables are compared with one another. This is thus a comparative calibration. For the example illustrated in FIG. 2, this means that the use of a beam balance for determining the sought mass m2 is a comparative measurement. If the upper beam 1 is horizontal, this means, if the lever arms are of the same length, that the mass m2 is the same as the known mass m1. The mass m2 is then determined and may be given, with the tolerances of the measurement system, bym2=m1.
Such a secondary calibration is known for determining the frequency response of pressure sensors.
To this end, dynamic pressure generators are known that are always equipped with a comparison sensor and therefore serve for secondary calibration, as described above. Such a dynamic pressure generator is known from numerous publications, such as                Kuhn; Werthschützky: Analysis of Dynamic Characteristics of Pressure Sensors, EMK TU Darmstadt,        Stefan Sindlinger: Einfluss der Gehäusung auf die Messunsicherheit von mikrogehäusten Drucksensoren mit piezoresistivem Messelement (Influence of the Housing on the Measurement Uncertainty of Microencapsulated Pressure Sensors having a Piezoresistive Measurement Element), dissertation, EMK TU Darmstadt, 2007        Sven Kuhn: Messunsicherheit elektromechanischer Wirkprinzipien zur Druckmessung and Optimierung von Verfahren zur Fehlerkorrektur (Measurement Uncertainty of Electromechanical Active Principles for Pressure Measurement and Optimization of Methods for Error Correction), dissertation, EMK TU Darmstadt, 2001,        Timo Kober: Analyse des Übertragungsverhaltens von Differenzdrucksensoren durch dynamische Druckkalibrierung (Analysis of the Transfer Behavior of Differential Pressure Sensors through Dynamic Pressure Calibration), article in Technisches Messen (Technical Measurement) February 2010,        Luca Tomasi: A new micromachined piezoresistive pressure sensor with dual range and self-test functionalities, dissertation, 2007 or        Adam Hurst: An Experimental Frequency Response Characterization of MEMS Piezoresistive Pressure Transducers, Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014        
These solutions may be schematically summarized in the illustration according to FIG. 3.
In this case, a pressure p is generated in a control volume 2 by way of a diaphragm 3. A piezoelectric actuator 4 is connected to this diaphragm 3 by way of a piston 8. If a voltage is applied to the piezoelectric actuator 4, said piezoelectric actuator expands. The expansion causes the diaphragm 3 to move. The diaphragm 3 compresses the oil with which the control volume 2 is filled and brings about a pressure increase.
Due to the properties of the piezoelectric actuator 4, the above-described development goals are able to be met using this method. The frequency of the generated pressure p may be varied by way of the frequency of the applied actuator voltage. The amplitude of the pressure p may be controlled by way of the amplitude of the voltage.
As already described, a comparison sensor 5 is also provided in this arrangement. The comparison sensor 5 has unknown dynamics. Due to its construction, very good dynamics of the comparison sensor 5 are however assumed. With reference to FIG. 1, this means that the deviation in the sensitivity over all frequencies corresponds to 0%. The reference value is the statically determined sensitivity of the comparison sensor 5.
In addition to the fact that the known pressure generator is provided for a secondary calibration, it has proven that the structure, which makes provision for the housing to be stationary, that is to say fixedly connected to a base, leads to the housing exerting uncontrolled and strong vibrations, as a result of which use for a primary calibration, in which the pressure p has to be calculated, is prohibited due to the large interfering influence on the pressure calculation. As illustrated in the mechanical circuit diagram according to FIG. 4, the housing 6 is fixedly connected to a base 7. This is intended to achieve a situation whereby only movement of the piston 8 is possible. The movement on the opposing side of the piston 8 and of the housing 6 is intended to be prevented by the base 7 and the connection of the housing 6 to the base 7, for example by way of a crossbeam 9. The base 7 in this case has a mass that is at least one order of magnitude greater than the mass of the housing 6.
As illustrated schematically in FIG. 5, however, the mass of the housing 6 and crossbeam 9 also vibrate therewith in practice. This occurs in a highly uncontrolled manner and is therefore not suitable for a primary calibration.
No standardized primary calibration method is known for the dynamic behavior of pressure sensors. Accordingly, there is also no dynamically calibrated pressure normal that could be used for a secondary calibration.